1. Field of the Invention
The present invention relates to a high current MOS transistor integrated bridge structure which optimizes conduction power losses.
2. Description of the Prior Art
A Graetz bridge rectifier circuit is often used to convert an electrical signal from alternating current to direct current. This rectifier circuit consists of two arms, or half-bridges, each containing two transistors in series.
A known type of rectifier circuit using integrated MOS technology is described U.S. Pat. No. 4,949,142.
This circuit provides a pair of MOS transistors on each arm of the bridge. These transistors are coupled together so that the source electrode of a first transistor in each arm is connected to the drain electrode of the second transistor in the arm. Coupling diodes are also placed between the source and drain electrodes of each transistor.
When this prior art circuit is constructed in integrated form, the coupled semiconductor regions, the transistor source and drain, the diodes, and the gate electrodes are fabricated on a single semiconductor substrate. This minimizes the substrate area used, and produces a higher speed circuit. A circuit constructed in this manner does optimize the area used on the semiconductor substrate, and ensures satisfactory circuit speed. However, this type of circuit cannot be fabricated so as to exhibit reasonable operating efficiency. The resulting monolithic integrated circuit has parasitic transistors which cause considerable power losses. While the circuit is operating, high current flow occurs, which causes excessive power dissipation through the parasitic devices and at connections between devices. This can result in breakdown of the connections, the parasitic transistors themselves, and adjacent integrated components forming the bridge. As a result, the bridge circuit fails to function.